1. Field of the Invention
Cable attachment system in which a single multi-strand cable is gripped so it can be rotated into resinous anchorage material in a borehole in the geologic formation of a mine passage with a length of the cable protruding into the passage for attachment of a variety of suitable devices to prevent failure of the geologic formation.
2. Description of the Prior Art
It is known that in the creation of underground passages in geologic material ground stresses or forces are released which cause strains in the geologic material surrounding the passage. The strain is reflected by the movements of the material and this is especially true in the roof and ribs of the openings. Many systems have been developed to resist these forces and reestablish a balance of stability by retarding the movement of the geologic material, not only in the roof but around the passage. An early form of roof bolt was disclosed by Ralson U.S. Pat. No. 2,850,937 on Sep. 9, 1958. In this disclosure the roof bolt embodies indicated means which can be seen and which convey information regarding whether or not the roof bolt is supporting its desired load in the mine.
References also are made to Emery U.S. Pat. No. 3,226,934 of Jan. 4, 1966, and Reusser U.S. Pat. No. 3,478,523 of Nov. 18, 1969, each directed to rock bolts having a load bearing plate for use in mine roof support. Other patents exist on roof bolts, fixtures, and on cable anchor fixtures which include Scott U.S. Pat. No. 4,378,180 of Mar. 29, 1993, Scott U.S. Pat. No. 5,253,960 of Oct. 19, 1993, as well as Gillespie U.S. Pat. No. 5,230,589 of Jul. 27, 1993.
Past practice in the mining industry has been to use mechanical type anchor bolts using steel heading, threaded rods, coupled if necessary for longer than seam height, and to use rebar steel anchored in resin where anchor problems exist. While these systems are still widely used, a recent trend has been to use cables in place of steel rods or rebars in the support systems. This has been particularly true where mine operators need to place long bolts in low seam heights, which requires coupling of the parts of the fixture and a weakening of the fixture due to the couplings. Couplings increase the cost and the threads of the rod produce stress concentrations which weaken the overall support. Cable type roof bolts, for example a 7-strand 5/8" or 1/2" diameter cable, can be readily placed in small diameter holes in low seams by bending the cable to obtain insertion and eliminate couplings. A difficulty with a cable support is it is hard to make an attachment to the cable which will allow rotation of the cable upon insertion. While rigid attachments can be placed on the cable, such as devices with tapered holes and locking jaws or socketed connectors, or perhaps, wrenches which use set screws or rigid clamping devices to hold the cable while spinning, are possible but are cumbersome, expensive and may interfere with attachment of other articles to the cable end.